1. Field of the Invention
This invention relates to spray booths used to coat workpieces with electrically charged resin powder.
2. Description of Related Art
Electrostatic powder paint spray booths are becoming much more common because of the hardened and improved finish provided by such methods, and the much reduced pollution resulting therefrom. This type of painting comprises spraying electrically charged paint powder onto workpieces that are at ground potential. The charged powder is attracted and adheres to the grounded workpieces, which are then baked in an oven to melt the powder, causing the powder to flow and cover the workpieces. Typically the pieces are hung on racks that pass through a spray booth, wherein a spray gun applies the powdered paint as the parts pass by. The booth is usually a rectangular box with entrance and exit openings, and a slot along the top to allow the hangers and parts to pass through the booth. The booths typically also have a filter system to remove and recover the excess powder that does not adhere to the parts, it being found that the powder will not stick to the pieces after a certain thickness of powder has built up on the part to neutralize the charge.
The spray gun and filter are usually a detachable unit so that it is easy to convert those parts of the spray booth system to a new color. Unfortunately the powdered resin also sticks to the inside of the rectangular booth, which is typically constructed from metallic walls that attract the charged paint powder. When the booth is converted to a new color, the inside of the booth must be cleaned of old powder to insure that none of the old color powder mixes with the new color powder. This is a costly, time consuming task that can shut down a whole assembly line for a long time.
U.S. Pat. No. 4,924,803 issued to Celant and Danish Reference No. 89/02788 by Andersen disclose a single plastic liner that covers the inside of the booth, wherein the liner can be removed and replaced by a different liner when a color change is desired. The single liner concept is difficult and dangerous to install. When the single liner is blown into place within the inside of the paint booth, air will leak out through the zippers and other necessary unsealable openings. Because the walls of the liner contain powder, the air that leaks out of the inflated cover will also contain powder. The powder is toxic, wherein the release of paint into the surroundings will create an undesirable environmental condition. Thus it is not practical to blow-up a single liner of the prior art with air to install it in the spray booth chamber. Additionally, both the Celant and Andersen devices require pressure or vacuum means to install and suspend the liners, thereby increasing the complexity and cost of the installation and overall assembly.